But the Amnesty report has revealed that since September, the Turkish authorities have rounded up scores and "possibly hundreds" of migrants onto buses and transported them to isolated detention centres where they have been held.

Refugees are seen in a Turkish Coast Guard ship after 152 refugees and asylum seekers were detained off the coast of Cesme Photo: Anadolu Agency

Refugees and asylum-seekers told Amnesty they were detained without explanation or legal justification in a camp in Düziçi in Osmaniye province or in the Erzurum removal centre in the province for up to two months without any external contact.

“When they put a chain over your hands and legs, you feel like a slave, like you are not a human being,” said one 40-year-old Syrian man who said he held in the centre for a week.

A spokeswoman for Brussels said the EU had taken note of the report and would look into the claims.

"The EU is not aware of individual cases of 'deportations' but the report will be considered with due attention, and followed up with the Turkish authorities, as appropriate," she said.

"The EU-Turkey joint action plan aims to prevent irregular migration and inform refugees of possibilities for orderly and legal migration, while increasing support to those living in Turkey, including through improving access to public services like education for pupils, to health services and participation in the economy.

"Removal centres" receive foreign nationals who have been found staying irregularly in a county, including those awaiting their deportation following a failed asylum application. The Turkish legislation provides for the establishment of such centres. The goal of the EU assistance is to improve Turkey's capacity to host a growing number of irregular migrants – and to make sure this happens in decent conditions."

The Turkish government has angrily rejected Amnesty's accusations, saying it "categorically denied" that any Syrian refugee in Turkey had been forced to return to their conflict-torn home.

"We categorically deny that any Syrian refugees were forced to return to Syria," a Turkish government official said, adding that all returnees were being independently interviewed by the UN refugee agency.

Amnesty has warned the EU is being "reckless" in not doing more to prevent the human rights abuses, while at the same time engaging in migration talks with Turkey and giving its government billions of euros.

John Dalhuisen, from Amnesty International, said: “It is shocking that EU money is being used to fund an unlawful detention and return programme.

“The EU must ensure that its funding and migration cooperation with Turkey promotes rather than undermines the rights of refugees and migrants.”